Clean-burning natural gas has become the fuel of choice for millions of consumers around the world because of its versatility and availability. Because natural gas is colorless and odorless, modern natural gas odorization procedures have been established as a means of saving lives and protecting property. By the 1940s, gas odorization was widely endorsed by the industry. It was determined that leak detection would save lives, and legislation was passed requiring the odorization of natural gas. Today, state and federal regulations concerning the odorization of natural gas place a great deal of emphasis on enforcement.
Natural gas odor levels are usually monitored by several techniques, including the room test and the use of a dilution apparatus such as an odor tester, odorometer or odorator. Although there are various procedures involved in odor-level determination, the most common mechanism used in the industry is the human nose. Because the objective is to determine the actual degree of odor, not the amount of odorant, the human olfactory sense continues to serve as the standard of pungency.
Systems for injecting odorants are well known in the prior art. Such systems typically include a pump for injecting an odorant into the pipeline, and some timer or other controller to effect actuation of the pump at predetermined intervals. Because it is important to know the total volume of odorant injected into the pipeline over the period of operation, more sophisticated systems in the art include verification devices to determine the quantity of odorant injected. One such injection system, designated by the Model No. NJEX-7100 and offered by the assignee of the present invention, included a positive-displacement pump for injecting odorant into the pipeline, a controller, a flow switch connected to the outlet side of the odorant pump, and an odorant inlet meter for metering the odorant to the pump. The controller tracked the flow rate of the gas in the pipeline using a flow signal, and this signal was also used to calculate the stroke rate of the pump. Monitoring was achieved by the flow switch and the inlet meter. In particular, the flow switch interfaced to a counter to provide a continuous readout of the number of strokes, and the meter served as an additional monitor by counting the number of times the meter was refilled. From the number of strokes and a preset pump displacement setting (in cc/stroke), the purported volume of odorant injected was calculated. The system also included appropriate alarm circuitry for signaling the user in the event of a malfunction.
While injection systems such as described above provided significant operational advantages and improvements over the prior art techniques and devices, they provided somewhat "coarse" odorant usage data. For example, such systems were not capable of precisely monitoring how much odorant was being used per pump stroke because despite the preset pump displacement setting, the actual odorant displacement per stroke changed due to pump efficiency variations, static pressure variations, check valve performance variations, line debris and variations in the density of the odorant. Such variations caused inaccuracies in the odorant usage data, especially where the system was operating over long periods of time and in harsh environmental conditions. While these systems did provide quantitative raw data for analysis, adjustment and accountability of the odorant usage, they did not have any capability to present such data in any type of useful format to facilitate audit or reporting of system operation. The systems, although quite sufficient for their intended purpose, were also costly and had to be operated by experienced personnel.
Accordingly, there remains a long felt need for improved odorant injection systems which overcome these and other problems associated with the prior art.